a. Field of the Invention
The invention relates to fluid samplers and more particularly to a purge system for fluid samplers.
B. Prior Art
In the field of water pollution control there is a need to take samples of rivers, sewers, drains and the like. In industrial hygiene applications, there is a similar need to sample industrial plants' liquid effluents. Often this is accomplished by automatic samplers in which a sample chamber is filled with a desired sample volume which is then transferred into sample containers for use in a testing device; a complete apparatus including sample chamber, containers and testing device being described in U.S. Pat. No. 4,098,305, assigned to the assignee of the present invention. After the test procedure is complete the sample is wasted.
In automatic samplers a plurality of sample chambers is frequently used, with a sample being taken periodically, perhaps every hour or more, perhaps every six hours. During this period, the nature of the sample may change slightly. For example, even a few parts per million of certain substances or a change of a few parts per million between samples may be a cause for concern. This means that the sampling apparatus must be sensitive and also that contamination of samples must be avoided and that cross contamination between samples be avoided.
In a prior co-pending application, Ser. No. 918,470, assigned to the assignee of the present invention, the problem of cross-contamination between samples in re-used sample containers was discussed. However, in the present invention our concern was for the intake channel which feeds the sample containers. This channel is frequently made up of hose, tubing, pipes and reservoirs between an intake source and a sample container.
One problem is that a small amount of the previous sample remains in intake channels of the prior art. When a subsequent sample is drawn into the intake chamber, a slight amount of sample cross contamination occurs. Frequently this is due to small kinks in the channel, or gravitationally uneven locales where tiny puddles of sample material may form. In other instances, sample material such as suspended solid material may merely adhere to the walls of the intake channel until a subsequent sample causes this material to move along with the new sample flow, again causing some sample cross-contamination.
Another problem is the introduction of biological material into samples, particularly the growth of algae between sampling intervals. If sampling times are more than a few hours apart, measurable amounts of algae may grow in the intake channel where tiny puddles of prior sample material resides. This algae would be swept along with the next sample to be introduced causing a source of contamination. It may also be possible for other undesired organisms to enter the intake channel between samples, since this channel is usually left in the fluid body to be sampled and is usually open for entry of suspended solid matter during the time a sample is drawn.
An object of the invention was to devise a fluid sampler in which the problem of sample cross-contamination in the intake channel could be eliminated. Another object was to avoid sample contamination by algae, or the like, or even larger organisms invading the intake channel.